Typically, copper electric wires are used for wire harnesses that are wired in a vehicle such as an automobile. When these wire harnesses are connected or the wire harness and an in-vehicle apparatus are connected, a terminal is attached to the copper electric wire of the wire harness, and this kind of terminal is typically attached to the copper electric wire by being crimped.
Typically, the terminal, which is crimped to the copper electric wire, includes a bottom plate on which a conductor part of the copper electric wire which is formed by twisting a plurality of copper strands is placed, and a pair of conductor tightening pieces which are provided adjacently to the bottom plate to hold the conductor part which is placed on the bottom plate.
When the pair of conductor tightening pieces are crimped inward, the conductor part of the copper electric wire is sandwiched between the bottom plate and the pair of conductor tightening pieces so that the terminal is crimped to the conductor part of the copper electric wire by this sandwiching.
In recent years, in consideration of the lightweighting of vehicles, and the easiness of material recycling, in addition to the lack of copper resource, it is considered to use aluminum electric wires to replace the copper electric wires. However, an oxide film formed on the surface of aluminum is thicker than that of copper, and for the aluminum electric wire, the contact resistance between the conductor part and the crimped terminal tends to become relatively higher.
Thus, to reduce the contact resistance between the conductor part of the aluminum electric wire and the crimped terminal, a method is adopted to strongly crimp a barrel of the crimped terminal to the conductor part of the aluminum electric wire to raise compression rate of the conductor part of the aluminum electric wire. When this method is used, because the conductor part of the aluminum electric wire is strongly crimped, the oxide film of the strands of the conductor part of the aluminum electric wire is broken and the contact resistance between the conductor part and the crimped terminal of the aluminum electric wire is reduced.
It is known that when water exists at the contact part (crimped part) where different kinds of metals (that is, the aluminum material and the copper material) contact, the two metals (aluminum and copper) dissolve into the water as ions, a potential difference between the aluminum material and the copper material is produced, and electrolytic corrosion occurs.
Thus, when the crimped terminal made of copper or copper alloy is connected to the conductor part of the aluminum electric wire, the crimped part of the conductor part of the aluminum electric wire crimped by the barrel of the crimped terminal is crimped at a high compression rate so that water is prevented from invading the contact portion where the conductor part of the aluminum electric wire and the barrel of the crimped terminal contact, and the occurrence of the electrolytic corrosion can be avoided.
However, even if the conductor part of the aluminum electric wire is crimped by the barrel of the crimped terminal, the waterproofing effect is not perfect. Thus, traditionally, as in a connecting structure disclosed in a patent document 1, insulating coating at the distal end side of an aluminum core line is peeled to expose an aluminum electric wire distal end, and by immersing the aluminum electric wire distal end in molten solder which is molten at approximately 300° C. by using, for example, Sn—Zn solder which is easy to be close to aluminum, coating solder attaches to and coats the surface of the aluminum electric wire distal end.
It is described in this patent document 1 that it is desirable that the coating solder which attaches to the surface of the aluminum electric wire distal end has such a thickness that a break will not occur because of the crimping of the wire barrel.
Further, a terminal metal fitting attached electric wire is disclosed in a patent document 2 for which without using anticorrosive material, the connecting part where an electric wire and a terminal metal fitting is connected is surely prevented from electrolytic corrosion. The terminal metal fitting attached electric wire includes an aluminum electric wire whose metal core line is covered with an insulating coating, a female terminal metal fitting which is made of a metal different from that of the core line, and is provided with a wire barrel which is connected to the aluminum electric wire, a solder seal which is formed of a solder which mainly includes a metal whose ionization tendency is close to that of the female terminal metal fitting, and to which the wire barrel is crimped while the core line, which is exposed by peeling a part of the insulating coating of the aluminum electric wire, is sealed by the solder, and a seal connecting part which connects the insulating coating which is adjacent to the exposed core line and the solder seal while the insulating coating and the solder seal is sealed.
Thus, it is described in this patent document 2 that the solder seal is crimped by the wire barrel in an overlap-crimping manner, and a crimping condition is set so that the solder seal will not break by this crimping.